In general, this invention relates to alarm-signaling devices of the type used to warn hospital attendants that only a predetermined amount of liquid remains in a container dispensing liquid intravenously into a patient. More particularly, it relates to such a device in which an attitude-sensitive transducer initiates the giving of an alarm signal.
It has long been recognized that there exists a need for a device to provide an alarm signal to alert hospital attendants that only a predetermined amount of liquid remains in a container dispensing liquid intravenously to a patient. Various patents each give a comprehensive explanation of the reasons why this need exists; see, for examples, U.S. Pat. No. 3,942,526 and U.S. Pat. No. 3,977,567.
In one class of known I.V. alarm devices, there is used a relatively simple arrangement wherein a spring suspends the liquid container. The biasing force of the spring causes the container to rise as liquid is dispensed, and an electrical switch is activated when the container reaches a predetermined position. Although simple in construction, the devices in this class are cumbersome and unreliable.
Other proposed devices suffer from the disadvantage of complexity of construction and attendant expense.
With reference to U.S. Pat. No. 3,977,567, the device disclosed therein incorporates a moving member, viz, a balance arm, that rotates rather than translating up and down as do the devices of spring supporting class. Similar to those devices, the balance arm has a portion that acts like a switch contact for initiating an alarm signal when that portion is rotated into alignment with a fork-shaped support member. At the lower end of the balance arm there are positioned along a straight line various holes including a hole for receiving a pin pivoting the balance arm to the support member. The other holes are used for holding the container and counterweights. To use this device, it is necessary to perform a number of manipulative steps defining a pre-balancing procedure. In this procedure, first, the balance arm is oriented in a predetermined, balanced relationship with respect to the support member by appropriately positioning a counterweight, and, then, the counterweight is moved to a different position thereby causing the balance arm to become unbalanced and swing until a stop member limits its angular movement. Following this procedure, liquid is dispensed from the container and the combined weight of bottle and liquid decreases. Eventually, a point is reached where a torque is imposed on the balance arm in a direction causing it to rotate back toward the pre-balance position. Another factor, apart from the above-described time-consuming pre-balancing procedure, bearing mention in a description of this patented device is that, as disclosed in the patent, it is intended for use with two of the standard sized bottles, viz, 500 cc and 1000 cc bottles. There is no disclosure as to use with the newer, much lighter plastic bags. Moreover, the ratio of the weights involved here is substantial, thereby rendering it difficult to adapt this device to handle such bags. In particular, an empty plastic I.V. bag typically weighs only 40 grams, plus or minus 4 grams. On the other hand, an empty standard 1000 cc bottle weighs 530 grams, plus or minus 21 grams.